c# - 如何将 ThenInclude 实现到 EF Core 自定义规范中？

Question

英孚核心 3.1
我见过Specification例如，并希望实现 ThenInclude 模式。

public static class QuerySpecificationExtensions
{
    public static IQueryable<T> Specify<T>(this IQueryable<T> query, ISpecification<T> spec) where T : class
    {
        // fetch a Queryable that includes all expression-based includes
        var queryableResultWithIncludes = spec.Includes
            .Aggregate(query,
                (current, include) => current.Include(include));

        // modify the IQueryable to include any string-based include statements
        var secondaryResult = spec.IncludeStrings
            .Aggregate(queryableResultWithIncludes,
                (current, include) => current.Include(include));

        // return the result of the query using the specification's criteria expression
        return secondaryResult.Where(spec.Criteria);
    }
}

我可以将其添加到字符串中，例如“User.UserRole.Role”，但我想实现对象。
也许那里不可能？

Answer 1

Includes前述成员ISpecification<T>被声明为

List<Expression<Func<T, object>>> Includes { get; }

问题是 EF Core Include/ ThenInclude链不能用 Expression<Func<T, object>> 表示.此模式在 EF6 中使用，它支持包含表达式内的特殊语法 ( Select ) 来解析集合元素。但是 EF Core 不支持开箱即用。

插入 EF Core 模式的最简单、最自然的方法是更改​​定义如下:

List<Func<IQueryable<T>, IIncludableQueryable<T, object>>> Includes { get; }

为具有 User 的实体添加样本属性(property)有 UserRoles收藏有 Role属性将是这样的:

Includes.Add(q => q.Include(e => e.User).ThenInclude(e => e.UserRoles).ThenInclude(e => e.Role));

和 Specify的对应部分方法实现将是:

var queryableResultWithIncludes = spec.Includes
    .Aggregate(query,
        (current, include) => include(current));